One would not suppose it, but every solid object, such as a steel knife, a wineglass, a lump of coal, is covered with a thin layer of water; it has also on its surface a very thin film of air. These can be removed by heating; but when the substance is again cold, the layers of water and condensed air return if it is left lying about. The amount thus adhering depends partly on the material of which the object consists, and partly on the extent of its surface; a large surface condenses more gas and water than a small one.

Now, the smaller a particle, the larger its surface in comparison with its volume; that is easily realized when it is considered that by powdering any material its surface is greatly increased, while its total volume remains unaltered. Particles of dust, therefore, which are very small, possess relatively large surface. Next, ordinary air which we breathe always contains the vapor of water; this is seen in winter when the glass panes of a window become frosted over with frozen water, deposited from the air in which it had previously existed as vapor. If air is cooled, it deposits some of its water-vapor. Another point to consider is that when air is compressed it grows hot, as every one who has pumped up the tire of a bicycle knows; and the converse of this is also true; when air expands against a resistance, it cools itself. Now imagine a glass globe full of air, saturated with water-vapor-that is, containing as much as it will hold at the temperature of the room. Suppose this air made to expand, by withdrawing some suddenly with a pump; then some of the water-vapor is bound to condense (for the air becomes colder), provided it can find anything to condense on. All air contains particles of dust, unless they have been filtered out by passing the air through cotton-wool. And each dust particle will become covered with a droplet of water, due to the adhesion of water to its surface, and the result will be a fog. Indeed, it is possible to count the number of dust particles in air by this means, as was shown years ago by Mr. John Aitken.

But it is not merely dust which will condense water vapor into liquid. Invisible particles, termed ions, will do the same. What is an ion?

For long, electricity was supposed to be a mysterious fluid, or rather, two mysterious fluids, one of which was called "positive," the other "negative." It has now been shown, thanks to the investigations of Sir J. J. Thomson, of Cambridge, that what was known as a current of "negative" electricity is, in actual fact, a stream of small particles moving with great velocity. These particles of electricity, known as electrons, can combine with matter; metals are such compounds; gases like oxygen and nitrogen have also electrons associated with them. When an atom of oxygen, of iron, or indeed of any substance, has been deprived of an electron, or has had an electron added to it, it becomes an ion. If the electric particle has been removed, it is said to be a positive ion; if the electron has been added, it is called negative. The word "ion" means "going," or "traveling"; such atoms are easily attracted to or repelled by electrified bodies, and they move rapidly toward them, or away from them, as the case may be; if the electrification of the body is negative-that is, if there is an excess of electrons adhering to its surface- it repels particles which have also an excess electron; if, on the contrary, the electrified body is electrified by having had electrons removed (and that is called positive electrification), then it will attract particles having an excess electron.

Now, when atoms of helium are expelled by the excessive force of a radium atom, they are moving, as has been said, with enormous velocity. In passing through air they collide with the molecules of oxygen and nitrogen, and convert some of the atoms with which they come into contact into ions-that is, they knock off electrons from some, while they add electrons to others. Both kinds become able to exert attraction on neighboring matter; and in presence of cooled water - vapor some of the watervapor condenses on these ions; round each ion a droplet is formed. If brightly illuminated, the row of droplets appears as a white streak, which can be photographed; it reveals the track of the moving helium atom. The motion soon

dies out; at ordinary atmospheric pressure the distance traversed does not exceed two inches, owing to the collisions

of the helium particles with the air molecules, and the consequent stoppage of their motion. The photograph reveals a number of short, straight lines radiating from the particles of radium from which the helium atoms are escaping; these consist of lines of vapor condensed on the ions of air produced by the bombardment of the air molecules by the rapidly moving helium atoms. Again, although we cannot see atoms, still their paths can be traced and their presence revealed.

Until recent years it was believed that there are some eighty kinds of matter which cannot be simplified; to these were given the name elements." Water, for instance, can be changed, on passing an electric current through it, into its constituents, oxygen and hydrogen; from glass it is possible to produce its constituents, namely, silicon, calcium, sodium, and oxygen; all these were, and are still, termed elements, for out of none of them was it possible to obtain any simpler form of matter. To each of these elements an atomic weight has been ascribed; thus, taking the weight of an atom of hydrogen as unity, that of oxygen is 16; of silicon, 28; of sodium, 23; and of calcium, 40; these are the relative weights of the respective atoms. Here is a list of the atomic weights of some of the elements:

Hydrogen, 1; helium, 4; lithium, 7; glucinum, 9; boron, 11; carbon, 12; nitrogen, 14; oxygen, 16; fluorine, 19; neon, 20; sodium, 23; magnesium, 24; aluminium, 27; silicon, 28; phosphorus, 31; sulphur, 32; chlorine, 35; argon, 40; potassium, 39; calcium, 40, etc. If these numbers be compared, it will be seen that they follow a certain order; thus, the eighth element after helium is neon, like helium an inactive gas; the eighth element after lithium is sodium, a soft, white metal like lithium; similarly, magnesium resembles glucinum; aluminium resembles boron; silicon, carbon; and so on. Argon, again, is the eighth element after neon, which it resembles, as it also resembles helium. There is another noticeable point. Niton has been mentioned as one of the products into which radium changes; the other is helium. Now, the atomic weight of radium has been very carefully determined; it is 226. As the loss of an atom of helium VOL. CXXVII.-No. 759.-46

of atomic weight 4 changes it into niton, the atomic weight of niton should be 226 minus 4, or 222; and the result of experiments by Dr. Whytlaw - Gray and the writer showed that that is the atomic weight of niton. We have here a clue to the structure of one element; and it is worth while seeing if other elements cannot be caused to change, and whether one of the products of the change will not be helium.

Radium changes spontaneously; how can other elements be induced to imitate it? Let us first think of compounds all of which are decomposable. Most compounds change into the elements of which they are composed if they are raised to a sufficiently high temperature, or if they are made to conduct an electric current. Elements, on the other hand, stand the highest temperatures which can be produced artificially without changing their nature, although all change their state; that is, the solid elements melt, and then change to gas; but the element remains. essentially the same; on cooling, the original substance is recovered. What may happen at the enormously high temperature of some of the stars is another thing; there is evidence, which cannot be treated of in the present article, which gives rise to the presumption that in the hottest stars many of our elements have no existence. Again, elements either refuse to allow an electric current to pass through them, like sulphur, or they conduct the current, like copper, and are not altered thereby.

Heat and electricity in motion are forms of energy; and the problem is how to impart a very large quantity of energy to a small quantity of an element. The most potent form of energy which we know—that is, the greatest amount of energy in the smallest spaceis that afforded by the spontaneous decomposition of niton, the first product from radium; it is capable of raising two and a half billion times its weight of water through one degree centigrade; or, by volume, twenty-four million times in about a month; for it takes about that space of time to "disintegrate." A gram, about the thirtieth part of an ounce, of niton will give off as much energy as five horses would if they worked for a month. But no one can

obtain a gram of niton; the amount with which the writer worked was only the millionth part of that quantity; it represents the work which would be done by a horse in twelve and a half seconds. Still, the space occupied by the niton is infinitesimal; a little tube no thicker than the finest hair and an eighth of an inch long would amply hold the niton.

Now, niton, it will be remembered, changes spontaneously; it expels atoms of helium moving with enormous velocity. Just as bombardment with the stream of bullets from a machine-gun destroys any object on which the bullets strike, so it may be conjectured that the stream of helium atoms may destroy the atoms of elements on which they impinge. To test this, some niton was dissolved in water; it was easy to prove that the gases produced consist mainly of oxygen and hydrogen, the elements of which the water consists. It was also easy to detect the helium produced from the niton; but it was with considerable surprise that it was found that the element neon was mixed with the helium.

Nature sometimes aids us in making experiments, although as a rule she places hindrances in our way; in this case she was kind. Mineral springs often contain niton, and gases escape from the water in large quantity. An investigation of the gas escaping from the mineral springs of Bath showed the presence of helium, as might have been expected, due to the disintegration of the niton; but the amount of neon in these gases greatly exceeds that of the helium.

Again, when niton is dissolved in a solution of sulphate of copper, some of the atoms of copper appear to be broken up by the rapidly moving helium atoms, and another element, lithium, appears to be the product. Other experiments showed that the elements silicon, titanium, zirconium, and thorium, as well as lead, when treated with niton, yield carbon as one of their products of decomposition. In fact, it must be inferred that just as there are elements which spontaneously change into others, so many of the ordinary "stable" elements can be broken down by appropriate treatment.

communication to the element to be changed of a large dose of concentrated energy; and the next step was to try if electric energy would have a disintegrating effect. Every one knows nowadays that it is possible, by means of "X-rays," to photograph the bones, and indeed the heart and the stomach, inside the body. An X-ray bulb is a glass flask with three metal plates in its interior, connected to the outside by wires. From one of these plates negative electricity in the form of cathode rays is made to stream; these rays hit another plate, placed at an angle, so that the X-rays pass out of the bulb; it is these which are used to take photographs. The third plate is the positive electrode. These bulbs are "run" for months before they become useless, hence they have received large doses of energy during their lifetime. Now, on examining the gas from the interior of several of these bulbs, old from use, it was found that helium was present. The air contains some helium; and it was not impossible, though unlikely, that it might have entered the bulb through the glass. But that idea was negatived by experiments made quite independently by Professor Norman Collie and by Mr. Hubert Patterson; each of them passed a stream of cathode rays through hydrogen; the rays impinged on the glass vessel; and after five hours both helium and neon were found in the gases pumped out of the bulb. Again, the helium and the neon might conceivably have entered from the outside air; but that was disproved by surrounding the bulb with an external vessel from which all air had been removed; helium and neon were still found in the gases which had been exposed to the cathode rays; none could have entered from without. On interposing a plate of aluminium, so that the cathode rays did not strike the glass, no neon was formed; the glass of the vessel appears to be essential to the formation of neon. Now, glass is a compound of silicon, calcium, sodium, and oxygen; presumably it is the oxygen which leads to the production of neon, although that has not yet been conclusively established; both Professor Collie and Mr. Patterson found that if oxygen is present along with the hydrogen in the bulb, and if the mixture is treated with cathode rays,

An atom of helium is 4 times as heavy as an atom of hydrogen; an atom of oxygen, 16 times; an atom of neon, 20 times. A reasonable explanation of what has been found would appear to be given by the supposition that four atoms of hydrogen have combined to form an atom of helium; that if oxygen be present, an atom of helium and an atom of oxygen combine to form an atom of neon. But the case is not quite so simple; for the atom of neon is not exactly 20 times as heavy as an atom of hydrogen, but 20.2 times. Whence comes the decimal .2? In all probability from the electrons, or atoms of electricity; we may therefore speculate that neon is a compound of hydrogen in

The case is by no means proved; but enough has been said to give some idea of the progress which is being made in the direction of ascertaining the nature of the elements. "Facts are chiels that winna ding," and it is necessary to account for the facts which have been described. The explanation may be wrong; but the human mind cannot rest content with retaining in the memory a mere catalogue of facts; theories are put forward, and it remains to be seen whether they will be justified by new facts. Such is the history of the progress of science; and whatever the explanation, the fact is incontestable that a new chapter in the history of chemistry-that is, in knowledge of the world around us-has been opened.

W1

HILE it is difficult to defend Cunningham Black, his conduct needs no explanation. That diablerie which spices all his writing is characteristic of the man himself; there is more than a hint of the satyr about him. The two waves of hair on each side of his forehead inevitably suggest horns, and the set of his eyes, the half-whimsical cynicism of his expression, are all in keeping with the popular conception of the hoofed devil. Lastly, his extraordinary thinness, which is emphasized by his prim, neat dress; his narrow, bony hands and feet, the curious squareness of his little shoulders, all heighten the impish effect of him.

As to the origin of the long campaign -that, too, is easily explained. Cunningham Black was the son of a bookseller, and although he had made himself acceptable to society by his cleverness and his wonderful adaptability, he was always a little over-assertive. He had not forgotten the bookseller's shop, and he continually persuaded himself into a contempt for those who moved so easily in ways which he had studied with long effort. Doubtless he tried very earnestly to despise these people with whom he loved to be seen.

Every one now knows the other protagonist. The unhappy Valetta, Duchess of Tottenham, has attained a celebrity she neither desired nor deserved. Her very tricks of manner and speech are familiar to the general public. Unhappy she certainly is, and for no fault of her own. There were no less than three Duchesses of Tottenham when the trouble began, and she was the younger of the two dowagers. She was, in fact, quite terribly poor for her position, and she cannot be blamed for staying with the Davidsons, or with any other people in whose houses she could really economize. Meanness in the matter of tipping the servants was excusable in a duchess.

Black was not in an unusually bad temper when the incident happened. He had lunched on the corridor-train, not to his complete satisfaction, but still sufficiently, and when he had found a firstclass smoking-carriage on the branch line and settled himself down to a very decent cigar, he was probably in a fairly comfortable humor. Then, just as the train was starting, Valetta was ushered with some ceremony into his empty compartment.

Black did not know that it was the Duchess; he did not know that the Duchess was going to the Davidsons. He only knew that a thin, middle-aged, rather expensively dressed woman in a pince-nez had been thrust upon him, and he resented it. He realized, too, the fact that she was treated with much deference by the attendant guard. There was an innate radicalism in Black which was always up in arms against this show of deference to the upper classes.

He had put up his long, thin feet on the cushion of the opposite seat, and he withdrew them very deliberately when he found that the intruding woman intended to enter that compartment and no other.

The train started immediately; the Duchess, already affronted, took her seat in the corner by the farther door, and Black put his feet up again and continued his cigar.

The Duchess coughed and let down the window. She had her back to the engine; Black was facing it, and he was immediately conscious of a draught. He scowled at his companion and turned up the collar of his overcoat.

The Duchess coughed again-a cough which perfectly expressed her dislike of the cigar and the smoker of it.

Black was exasperated. "Why travel in a smoking-carriage, madam, if you object to the smell of smoke?" he asked, acidly. "The train is not full."

"I did not notice," said Valetta, and